[Qt-interest] QDoubleSpinBox can't undo change after losing focus, is this a bug?

[liang jian]

    To produce this problem, open Qt Designer, create a widget and
drag a spin box and a double spin box to this widget. Press Ctrl+R to
preview it, change the text in the spin box to a different value and
then click the double spin box, change its value too, return to the
spin box and right click to show the context menu, you will see undo
menu item is enabled, but if you go back to the double spin box and
right click to show the context menu you will see that the undo menu
item is grayed (I think at that time it should be enabled).  I can
produce this problem in both my windows 7 and ubuntu 11.04 system, is
this a bug or a feature?